The present invention relates in general to the art of earth boring and, more particularly, to a down-the-hole air operated rock drill hammer. Air operated rock drill hammers generally include an annular body portion having a central chamber. A piston is mounted in the central chamber for axial movement to provide hammer blows. A bit is connected to the annular body for receiving the hammer blows. Passage means are provided in the annular body and the piston for delivering driving air to move the piston and alternately strike the hammer blows and recover therefrom. The piston is alternately moved linearly by the presence of air alternately at each end of the piston. The piston strikes the bit at the lower end of travel for impacting the earth formations. The air is controlled by the piston motion.
Prior art rock drill hammers have used extensive and complex ports and porting to supply air to the piston. The piston is usually the valve that controls the air to the chambers on each end of the piston. The designs include two ports into the piston and as well as a multitude of passages and ports that are almost impossible to describe. Some designs involve extensive machining on the piston diameter with staggered ports and passages in the cylinder case.